have you ever wanted to hold your Macbook sideways (like a book)? (I bet you probably haven't, actually.) But now you can!
A developer by the name of Nathan Stevens has released Mac Screen Rotate, and the app does exactly what it says. The app cost $5, and it works best on the Air or the 13" Macbook. nathan thinks that anything larger is too awkward to hold.
The app rotates the screen and the trackpad, and it also assigns several shortcuts so you can switch back and forth easily.
BTW, I'm pretty sure that OSX already had this feature. You might want to try this before parting with your $5. I suspect that the built in feature might not rotate your trackpad, though.
P.S. If anyone wants to try this on a 17" Macbook Pro, please take a picture. I wanna see it.